340 HORACE W. STUNKARD 



received in the course of the stud}'. An attempt was made to 

 determine whether in Amblystoma a segmentation of the neural 

 crests is regularly and uniforml}^ present, and to compare this 

 division with that of the neural plate. Further, to determine, 

 if possible, which, if either, is of metameric significance. The 

 persistent doubt regarding the accuracy of the observations of 

 Locy and Hill on chick embryos makes a reinvestigation and 

 confirmation of their work very desirable. 



The study of Amblystoma was made upon several hundred 

 embryos, collected near Champaign-Urbana, Illinois. The entire 

 series of changes involved in the formation and closure of the 

 neural tube was repeatedly observed under the binocular. To 

 make more careful observation, parts of the neural crests and 

 medullary plate were dissected and observed from all angles and 

 with various means of illumination. For material to supple- 

 ment the study of living specimens, embryos at all stages of 

 development from the wide-open to closed neural tube were 

 killed in various fluids and sections were cut in transverse, 

 frontal, and sagittal planes. 



In Amblystoma, as the blastopore narrows to a small oval 

 structure, a distinct longitudinal groove forms anterior to it. 

 In a few specimens the groove appears to extend to the lip of the 

 blastopore, but in the large majority of embryos when the groove 

 is first formed a short distance separates it from the blastopore. 

 In some embryos the groove extends anteriorlj^ and posteriorly 

 in a continuous manner, so that with the closing of the blastopore, 

 it forms the definitive neural groove. In other specimens, 

 however, another faint groove, usually shorter than the first, 

 may appear anterior to it. This observation agrees with that of 

 Griggs ('10), although the appearance of the grooves does not 

 show the regularity or constancy reported by him. The first of 

 these grooves he termed the posterior germinal depression and 

 that anterior to it the anterior germinal depression. The groove 

 formed by the concresence of the lateral lips of the blastopore 

 he called the blastogroove. There is considerable variation in 

 the uniformity and regularity with which these grooves appear, 

 often separate germinal grooves are entirely absent and the 



